This invention relates to a vehicle lateral movement stabilizing device for controlling a brake assisting device for increasing the frictional force of the wheels or the vehicle to the road surface during braking so that the stability and turnability of the vehicle will improve.
On a frozen road on which the friction coefficient μ is extremely small, even if hard brakes are applied to the wheels, due to tire slip, it is difficult to obtain a sufficient frictional force to the road surface. On the other hand, use of spike tires are prohibited for the reason that they abrade roads and cause dust pollution. Thus, besides normal brakes (first braking force) that act on the wheels, a brake assisting device which increases the friction coefficient μ or effectively acts even if the friction coefficient μ is small is desired.
An ABS (antilock brake system), which is widely known as a system for efficient braking of wheels, is a system in which the reduced friction coefficient μ is recovered as much as possible by interrupting braking at short intervals to efficiently carry out braking. But on a frozen road or the like, since the friction coefficient μ is small, a system is desired which can stop the vehicle more effectively at a short braking distance.
As a measure to directly increase the friction coefficient μ, a slip preventive assisting device is proposed by JP patent publication 7-309101 (publication 1). In the device of this publication 1, the friction coefficient μ is increased by scattering ice particles (or a mix of water and ice particles) between the tires and the road surface because if sand is scattered for slip prevention, this may cause dust pollution and environmental pollution.
As a means for effectively obtaining frictional force even with a low friction coefficient μ, an emergency braking device is proposed by JP patent publication 8-156760 (publication 2). In the device of publication 2, a second braking means is provided which comprises a friction material which can directly engage the road surface and a hydraulic cylinder for operating the friction material. If the friction coefficient μ of the road surface is detected so small as to cause slip state by normal braking, the second braking means is activated to engage the friction material on the road surface to stop the vehicle.
The slip preventive assisting device of publication 1 can shorten the braking distance by scattering ice particles to increase the friction coefficient μ between the tires and the road surface. The emergency braking device of publication 2 also can shorten the braking distance by pressing the friction plate against the road surface to obtain frictional force of the vehicle for the road surface.
But either of the devices of publications 1 and 2 is used only to stop the vehicle by shortening the braking distance. No mention is made whatsoever as to how they are used to improve stability and turnability of the vehicle. Generally, during travel, a vehicle makes lateral movement in the range of the frictional force between the road surface and the tires when the steering wheel is operated. Thus, if the friction coefficient μ is extremely small, lateral movement of the traveling vehicle is significantly impaired, so that the travel stability and turnability of the vehicle will fall markedly. Thus, in order to improve travel stability and turnability, a measure to ensure lateral movement even on a road surface having a small friction coefficient μ such as frozen road has been desired. But such a proposal has never been made heretofore.
An object of this invention is to provide a lateral movement stabilizing device by which the frictional force of the wheels or the vehicle to the road surface can be increased with simple members, lateral movement of the vehicle is ensured, thereby improving travel stability and turnability.